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TECHNICAL PAPERS

Understanding Limits on Fin Aspect Ratios in Counterflow Microchannel Arrays Produced by Diffusion Bonding

[+] Author and Article Information
Brian K. Paul

Department of Industrial and Manufacturing Engineering, Oregon State University, Corvallis, OR 97331

Patrick Kwon, Ramkumar Subramanian

Department of Mechanical Engineering, Michigan State University, East Lansing, MI 48824

J. Manuf. Sci. Eng 128(4), 977-983 (Mar 07, 2006) (7 pages) doi:10.1115/1.2280672 History: Received April 07, 2005; Revised March 07, 2006

This paper investigates the manufacturability limits of fin aspect ratios within two-fluid counter-flow microchannel arrays based on the stress state between laminae during diffusion bonding. In prior papers, it has been shown that the diffusion bonding of two-fluid systems by microlamination can result in regions of the device that do not directly transmit bonding pressure and, consequently, result in unbonded regions leading to device leakage. A finite element model is used to analyze the stress state between laminae during diffusion bonding. The stress state is used to determine the critical stress necessary for diffusion bonding to occur in areas not receiving direct bonding pressure. Model results are compared with experimental results over a wide range of counter-flow geometries. It has been found generally that a compressive stress state must exist in every part of the geometry in order to produce leak-free bonds. Implications of this finding on the design of two-fluid microchannel arrays are discussed.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Microlamination scheme used to fabricate a dual micro-channel array. Arrows show direction of flow.

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Figure 2

An exploded view of the two-fluid counter flow microchannel array investigated in this study

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Figure 3

Top view of a counter-flow microchannel array comprised of microchannel and fin laminae. The necked-regions of the device are highlighted in gray.

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Figure 4

Cross-section of a microchannel neck at cross-section AA in Fig. 3

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Figure 5

Cross-section of a diffusion-bonded counter-flow microchannel heat exchanger showing sections through which the bonding pressure: (A) Was transmitted; and (B) was not transmitted. Cross-section (B) resulted in leakage between the two fluids.

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Figure 6

Geometry of the test coupon studied in this paper and verified by leakage testing

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Figure 7

Specific critical dimensions of the test article used in this study

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Figure 8

(A) Zoom in view of S33 stress contours for one of the microchannels. (B) S33 stress contours from FEA on counterflow microchannel model.

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Figure 9

(A) S33 stress countours on test coupon with h=0.1524mm and a=1.70mm. (B) S33 stress countours on test coupon with h=0.1524mm, and a=1.30mm.

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Figure 10

(A)–(C) Micrographs of test specimens consisting of 508μm thick laminae: (A) 5.08mm span (50×); (B) 3.175mm span (50×), and (C) 2.54mm span (50×). (D)–(F) Micrographs of test specimens consisting of 254μm thick laminae: (D) 5.08mm span (50×); (E) 2.54mm span (50×), and (F) 1.524mm span (50×).

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Figure 11

Mild stress variations at the neck region on Case 7

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Figure 12

A plot of the experimental results showing the conditions under which bonding did and did not occur. Bonding conditions for all of these samples were 5.86MPA at 900°C for two hours. The boundary line shows the rough conditions under which the modeled stress was near zero.

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Figure 13

A plot of the experimental results showing the aspect ratios under which bonding did and did not occur. Bonding conditions for all of these samples were 5.86MPA at 900°C for two hours. The boundary line shows the rough conditions under which the modeled stress was near zero.

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